Mendelian Genetics

Important Terms  Heredity- The passing down of traits or characteristics from parent to offspring.  Genetics-The study of heredity or how traits are inherited  Trait- A physical characteristic or attribute that is passed down from parent to offspring. –Example-Hair color, Eye Color, Hitchhikers thumb.

Checking for Understanding 1. What is a physical characteristic passed on from parent to offspring? 2. What is the passing down of traits from parent to offspring? 3. What is the study of Heredity?

Mendel and Heredity  Gregor Mendel was born back in 1822 in Austria.  Grew up on a farm with lots of plants  Joined a monastery at 21 years old -Monastery is a place where monks study religion  Did a lot of research  Used Pea plants for research.  Research helped to make him the father of modern Genetics

Why Pea Plants?  Mendel studied the heredity of pea plants because they reproduce quickly, unlike humans, who take many years to become sexually mature.  Pea plants also have a lot of different traits.

Checking for Understanding 1. Who is the father of modern genetics? 2. What kind of plant did he use?

Plant Pollination  Plants have both male and female parts.  Can reproduce 2 ways –Self Pollination –Cross Pollination  Pollination - The joining of a male cell (pollen) and a female cell (egg) to make a plant embryo

Plant Pollination Continued  Self Pollination –This is where a plant’s pollen fuses with it’s own egg.  Happens when there are no other plants nearby to mix with.

Plant Pollination Continued  Example: A single pea plant’s pollen fusing with it’s own egg.  Non-Example: Pea plants that are right next to each other exchanging pollen.

Plant Pollination Continued  Cross Pollination –This is where 1 plant’s pollen mix with another plant’s egg.  Can happen many ways- –Bees, Wind, Contact, Human intervention

 Example: 2 flowers exchanging pollen.  Non-Example 2 flowers close to each other still fusing their own pollen with their own egg. Plant Pollination Continued

Checking for Understanding 1. What is the joining of plant male and female cells called? 2. When 2 different plants male and female cells join what is it called? 3. Using Arrows draw an example of Self and Cross pollination and label them

Important Terms  Genes- One set of instructions for an inherited trait. –Genes are general and talk about whole attributes, not specifics.  Example-Hair color, Eye Color, Nose Shape  Non-example-Brown Hair, Green Eyes

Terms continued  Alleles- Different versions of the same gene. –Alleles are specific where Genes are general. –The genes for eye color have many different alleles (brown, blue, green, hazel).  Example-Brown Hair, Blue Eyes, Cleft chin  Non-Example- Hair Color, Eye Color.

Terms continued  Dominant- The trait that is observed or the trait that overpowers the other trait. –In most cases one allele is dominant over the all others for a particular gene. –Example: The allele for brown eyes is dominant over blue, green, and hazel.  Recessive- The allele that is covered up by the dominant allele. –Example: Having a black hair allele and a blond hair allele and the black hair wins.

Checking for Understanding 1. What is a different version of the same gene called? 2. What is the allele called that overpowers the other allele? 3. What is the allele called that is overpowered? 4. Chin Shape, Blue Eyes, Brown Paper, Which one of these are a gene?

Mendel’s Experiments  Mendel wanted to study how the pea plants inherited height.  Mendel cross pollinated short and tall plants.

Mendels’ First Experiment  How? –Didn’t allow plants to self-pollinate –Removed male parts from female plants –Chose specific plants to cross –Mendel brushed the pollen of one plant onto another. Femalepart Transfer pollen Pollengrains Maleparts Cross-pollination

Mendel’s Experiments  Mendel made sure the plants he crossed were true-breeders. –This means the tall plant had tall parents, grandparents, great grandparents, etc. Similarly, the short plant came from a long line of short plants.  Mendel called his first experimental plants the P1 generation, for “first parents.”

Checking for Understanding 1. What was the trait that Mendel investigated first? 2. What did Mendel call the first experimental plants? 3. What type of pollination did Mendel perform on the first experimental pea plants?

Mendel’s Results – First Generation  The babies of the P1 generation are called F1  Mendel noticed that ALL of the babies of the P1 generation grew up to be TALL.  The allele for shortness seemed to disappear.  Mendel thought this was strange, so he allowed all of the F1 generation to self- pollinate.

Checking for Understanding 1. What was the babies of the P1 generation called? 2. What did all the babies of the P1 generation look like? 3. What kind of pollination did Mendel allow the babies of the P1 generation to do?

Results: Second Generation   The resulting babies of the self- pollinating F1 generation are now called the F2 generation.   Mendel planted more than 1000 plants in the F2 generation.   When they grew up, Mendel noticed that 75% of the plants were tall and 25% were short.   The shortness trait reappeared in the F2 generation.

Checking for Understanding 1. What were the babies of the F1 generation called? 2. What percentage of the babies were tall? 3. What percentage of the babies were short?

More Important Terms  Probability - The relative frequency with which an event occurs or is likely to occur, typically expressed by a ratio. –Example: You have a 1:1 chance of tails landing up when you flip a coin.

 (P1)- Short pea plant bred with Tall pea plant.  (F1)- All the offspring were tall in the F1 generation.  (F2)- 3 out of 4 offspring of F1 were tall and 1 out of 4 was short. Short pea plant Tall pea plant All tall pea plants 3 tall: 1 short P1P1P1P1 F1F1F1F1 F2F2F2F2

Results: Second Generation  Mendel did this same experiment with 6 other pea plant traits and got the same results. –Height –Seed Shape –Seed Color –Seed Coat Color –Pod color –Pod Shape –Flower Position  One trait showed up more than the other in a ratio of 3:1. Mendel called this trait the dominant trait and the other, the recessive trait.

Results: Second Generation

Checking for Understanding 1. How many total traits did Mendel test for? 2. What was the ratio that Mendel came up with? 3. What is the relative frequency with which an event occurs or is likely to occur?

Even More Terms  Phenotype- is the physical expression of a gene. –Ex: plant height  Genotype- is the genetic combination of alleles that you inherit from your parents. –We denote genotype with letters. –The letters have to be the same for the same trait. –Capital letters denote dominant traits. –Lower case letters denote recessive traits.  Ex: B for Black hair, b for brown hair

Even More Terms  Homozygous- is when an individual has the same alleles for a trait. –Ex: I have 2 blue eyed alleles in my genotype. It could be TT for dominant trait, or it could be tt for recessive trait.  Heterozygous- is when an individual has different alleles for a trait. –Ex: I have different alleles for hair color; brown and black. 1 letter will be capital and the other will be lower case. (Bb)

Checking for Understanding 1. What is term for the genetic combination you receive from your parents? 2. What is the term for when you have 2 of the same alleles for a trait? 3. What is the term for when you have 2 different alleles for the same trait? 4. What is the term for the physical expression of a gene?